This application is based on Japanese patent application No. 8-90539 filed on Mar. 19, 1996, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a polishing machine for polishing a subject such as a semiconductor wafer, and more particularly to a polishing machine having a dresser for dressing a polishing cloth.
b) Description of the Related Art
A polishing process is performed, for example, in order to planarize the interlayer insulating film formed on the surface of a semiconductor wafer. A known conventional polishing machine polishes a wafer by pressing it to a polishing cloth which is fixed to a rotary platen.
As the number of wafers polished with such a polishing machine increases, the polishing cloth is filled or choked up with polishing agent, scraped-off particles and the like. The polishing cloth may be deformed or abraded by rotation or load of wafers. With these reasons, the polishing performance may be degraded such as lowering a polishing speed, and a wafer may be damaged or contaminated.
A dressing function of reconditioning a polishing cloth choked up with foreign materials has been added to a polishing machine (refer to JP-A-4-364730 and JP-A-7-254578).
FIGS. 12 to 19 illustrate an example or a conventional polishing method for a polishing machine having a dressing function. A polishing machine 10 has a platen 12 to the surface of which a polishing cloth is adhered and a wafer receptacle 14 mounted near the platen 12. As shown in FIG. 19, a dresser 24 held by a dresser holder 22 is movably mounted on the polishing machine 10. This dresser 24 is not shown in FIGS. 12 to 18 for drawing simplicity. As a dressing tool of the dresser 24, one of a wire brush, a resin brush, a diamond disk conditioner and the like is used.
As shown in FIG. 20, a wafer holder 18 can hold a wafer 18 at the inside of a guide 26, by a vacuum chuck or the like, and is made movable so that the wafer holder 18 can press the wafer 18 against the polishing cloth on the platen 12 while being rotating by its rotary shaft 28.
At the process shown in FIG. 12, a subject wafer 16 is placed on the wafer receptacle 14, and at the process shown in FIG. 13 the wafer 16 is sucked by a vacuum chuck and held by the wafer holder 18.
Next, at the process shown in FIG. 14, the wafer holder 18 holding the wafer 16 is moved to the central area of the platen 12. At the process shown in FIG. 15, the wafer holder 18 is lowered to press the wafer 16 against the polishing cloth on the rotating platen 12. Polishing agent is supplied from a dispensing nozzle 20 onto the platen 12. The wafer 16 rotated and held by the wafer holder 18 and pressed against the polishing cloth is therefore polished.
After polishing, at the process shown in FIG. 16 the wafer holder 18 raises the wafer 16 from the platen 12. At the process shown in FIG. 17, the wafer holder 18 holding the wafer 16 is moved to the wafer receptacle 14 and unloads the wafer 16 down into the wafer receptacle 14 through release of suction by the vacuum chuck or through application of water pressure.
At the process shown in FIG. 18, the wafer holder 18 is moved to the initial position. At the process shown in FIG. 19, the dresser holder 22 moves the dresser 24 to the area over the platen 12. Thereafter, the dressing tool of the dresser 24 is pressed against the polishing cloth on the rotating platen 12 to dress the polishing cloth while the dresser 24 is rotated. In this case, cleaning liquid such as pure water may be supplied from an unrepresented pipe to clean the polishing cloth.
After dressing, the process returns to the process shown in FIG. 12 to execute a polishing process for the next wafer in the manner described above. Dressing may be performed after a plurality of wafers are polished, not by performing it each time a single wafer is polished.
The following properties (1) to (4) are generally required for dressing.
(1) brushing or lapping away choked foreign materials in polishing cloth (lapping) PA1 (2) removing foreign materials on polishing cloth (surface cleaning) PA1 (3) providing plastic deformation for elastic polishing cloth or other cloths (pressing) PA1 (4) raising naps of fibered polishing cloth or other cloths (uniforming)
Various kinds of dressing tools have been proposed. However, none of them can satisfy the requirements of the properties (1) to (4) at the same time, and only one or more properties can be provided.
For example, if a diamond disk conditioner having a large abrading ability is used as a dressing tool, scraped-off polishing cloth fibers and diamond grains are Left on the polishing cloth so that the wafer may be damaged or contaminated. If a dressing tool having no cleaning ability is used, contaminated polishing agent is supplied to the subject wafer during dressing.
Furthermore, since the conventional dressing process is performed independently from the polishing process, throughput of both the processes is lowered if the polishing performance is not stable.